Acoustical panel construction



p 1963 J. H GILDARD m, ETAL 3, 0 ,98

Filed Aug. 31. 1960 ACOUSTICAL PANEL CONSTRUCTION 2 Sheets-Sheet 2INVENTORS. JHP7S H.6ILDAEDJZZ' 9 PJ'Cf/Hko 0. unnamed United StatesPatent 3,iitl3,9 7 ACQUSTHCAL PANEL CUNSTRUCTHUN lames H. Gildard ill,Baltimore, and iiiichtu'd D. Lernrnernian, Gibson lsiand, Md, assiguorsto hoppers Company, inc a corporation of Delaware Filed Aug. 312, 196i),tier. No. 53,tl'7$ 12 Claims. 3. 181-63) This invention relates toacoustical panel construction and, more particularly, to theconstruction of acoustical panels for use in installations in which suchpanels are exposed to high velocity gas flow such as in inlet andexhaust ducts for jet engine exhaust facilities.

It is well known in the prior art that materials such as glass fiber,mineral wool and the like provide excellent sound absorbing media. Suchmaterial in blanket form is typically packed into enclosures behindperforated face sheets which serve the dual function of providing adurable facing for the blanket while at the same time permitting theentry of sound waves therethrough for absorption by the blanketmaterial. The face sheets for such enclosures or as they are generallytermed, panels, are typically constructed of such materials as metal,asbestoscement board, hardboard or the like.

When the simple construction outlined above is used to absorb soundfrequencies in industrial applications, an added problem sometimes evenmore severe than that of sound absorption often presents itself. Thus,when these acoustical panels are exposed to sustained high velocity gasflow in excess of 200 feet per second whether the gas velocity path beparallel to the panel, perpendicular thereto or at some intermediateangle of incidence, there arises the danger of losing the fibrousblanket material by having it literally blown out of the panel throughthe perforations in the face sheet.

Accordingly, it is an object of the present invention to provide meanswithin an acoustical panel to protect the sound absorbing materialtherein from the destructive elfects of high velocity gas flow.

Another object of this invention is to provide a protective laminationof dissimilar materials covering the sound dissipating medium in anacoustical panel exposed to high velocity gas flow whereby the effectiveflow resistance of the lamination serves to deflect the high velocitygases from the sound dissipating medium or, at least, to reduce thevelocities of those gases reaching the sound dissipating medium.

An additional object of the invention is the provision of a uniquecombination of materials yielding sufficient flow resistance to highvelocity gases to prevent fiber blowout but yet not so great as toprevent the conduction of sound waves thereth-rough to enable absorptionby the blanket.

Still another object of this invention is to provide a velocityresistant lamination for use in an acoustical panel to protect the sounddissipating medium which lamination at one and the same time resists theerosive forces of high velocity gas flow and yet serves to enhance theacoustical qualities of the sound dissipating medium.

The general purposes of this invention as set forth above are attainedby providing a device for the attenuation of sound comprising incombination an enclosure having a portion of the surface thereofperforate for the communication of sound pressure waves from theexterior to the interior of this enclosure to reach sound dissipatingmaterial disposed therein and means transparent to sound pressure wavesheld in place between the perforate portion and the sound dissipatingmaterial to deflect or at least to reduce the velocity of gas streamflow incident upon the perforate portion and thereby prevent the erosionof the sound dissipating material during sustained exposure to highvelocity gas flows.

Other objects will be in pant obvious and in part specifically pointedout in greater detail in the following description wherein:

FIGURE 1 is a transverse sectional view along line ll through anacoustical panel constructed in accordance with the preferred embodimentof the present invention,

FIGURE 2 shows a plan view of the panel in FIGURE 1 with a portionthereof broken away,

FIGURE 3 is an enlarged view of the manner of unification of thelamination of FIGURE 1,

FIGURE 4 is a transverse sectional view along line lVlV through anacoustical panel embodying a modification of the present invention,

FIGURE 5 shows a plan view of the panel in FIG- URE 4 with a portionthereof broken away, and

FIGURE 6 is an enlarged View showing the manner of unification of thelamination of FIGURE 4.

Referring to the drawings, wherein like reference characters designatelike or corresponding parts throughout the several views, numeral 11makes reference in FIG- URES 1 and 2 to an acoustical panel into whichhas been incorporated the novel construction of the present invention.

In typical panel construction, as shown in FIGURES l and 2, the sounddissipating medium i2. (illustrated herein as glass fiber in blanketform) is enclosed within a metallic frame structure formed by sidemembers 13 secured, as by welding, to end members 14, and covered on theone side with a non-perforated metallic sheet 16 and on the other sideby a face sheet 17 of conventional perforate metallic plate. In generalthe frame members, side members 13 and end members 1 are formed fromchannel stock and are assembled with their flanges directed outwardly ofpanel ill to facilitate assembly with other panels, In the event thatpanel 11 is made in a very large size, cross pieces (not shown) areemployed to strengthen the panel construction.

Such panels are used to reduce noise particularly in industrialapplication by lining the walls of ducts, tubes, passageway and rooms inwhich the sound problem occurs. In other applications, the panels arearranged in spaced parallel relationship dividing such ducts, tubes, orpassageways into narrow passages for some distance. In the latterapplication the panels have perforate plates on both faces of the panel.By using these arrangements, the perforate pontion such as face sheet 17of the panel it are exposed to the sound pressure waves which passthrough the perforation l8 and dissipate their energies in the glassfiber blanket 12. The degree to which the sound energy is dissipated isdependent, of course, on the frequencies of vibration and the eificiencyof the sound dissipating medium at those frequencies.

The construction and operation as described up to this point, isconventional. However, should such construction be employed in thepresence of gas stream flow of the magnitude encountered in modern jetengine exhaust facilities (velocities in excess of 200 feet per second),the sound dissipating medium in this case the fibrous materialcomprising blanket 12 would be quickly eroded being blown out of thepanel bit by bit through perforations it; in face sheet 17.

To prevent this destruction, blanket 12 is protected by laminatedconstruction =19 which is transparent to sound pressure Waves and whichis mounted between the perforated portion, face sheet 17, and the sounddissipating material, blanket 12. As shown in the drawings, thislaminated construction 19, shown in detail in FIG- URE '3, consists ofglass fiber cloth 20 sandwiched between layers of Wire screen 21 and 22.There are, of course, certain limitations to be observed in theselection of these materials. The first limitation is in the arcane?allowable increase in the effective acoustical resistance of theperforations 18 which may be effected by the positioning of laminatedconstruction 19 adjacent perforations '18. If laminated construction 19contributes too great a flow resistance, the effective acousticalresistance of perforations 18 is increased too much with consequentreduction in the acoustical qualities of panel ll. On the other hand, iflaminated construction 19 provides too small a flow resistance therewill be insufficient protection against the erosion of blanket 12 byhigh velocity gas streams. It has been determined that the criticalrange of permissible acoustical resistance for the glass fiber cloth 2%)is from 37 rayls (1 rayl is that resistance involved when a pressure ofl dyne per sq. cm. causes a linear flow of 1 cm. per sec. of standarddry air). Within this range, optimum results are obtained (4 rayls) bythe use of glass fiber cloth having a thread diameter of .006" and aweave of 34 threads per inch in one direction and 32 threads per inch inthe other. This weave allows good entry of sound waves while beingsufficiently tight to prevent the sifting out of small fibers that maybecome detached from bianket 12. The close mesh wire screens 21 and 22are usually made of wire having a diameter of .011 and having 18 wiresper inch in one direction and 14 wires per inch in the other. This wirediameter is chosen as it is suf ficently large so as not to cut theglassiiber cloth 29, yet not so large as to be overly expensive. So faras the close spacing is concerned, this serves a particular purposeto beelaborated upon below.

In order to prevent the destruction of lamination 19 from flapping andfraying (Wind-flap) under the application of the velocity forces of thegas stream, a combination is made of glass fiber cloth 2t? interposed between the wire screens 21 and 22 by fastening them together in quiltfashion by the application of conventional staples 23 as shownapproximately every four inches in both directions. This unification bymeans of staples 23 enables lamination 19 to withstand theself-destructive whipping action (known in the art as wind flap) towhich it is subjected in use, an action similar to that commonlyexperienced by flags on display in high winds.

In the embodiment shown in FIGURES l, 2, and 3, the lamination 019 isassembled in panel 11 byinterposing it as a quilted unit between facesheet 17 and upper flanges 24, 2.6 of members '13 and 14 respectively atthe edges of face sheet 17 and clamping lamination 1-9 in place by meansof assembly rivets or bolts 27. 1.1 this manner, lamination 1 9 isrestrained only along the edges of panel 11.

While it would seem possible to select a given weave and weight of glassfiber cloth 24} which by itself would provide the correct flowresistance and also perhaps provide the necessary protection againstfiber blow out, it has been found in actual practice that screens 21 and22 are required to perform the Very necessary task of preventing glassfiber cloth 20 from being punched through as a result of being poundedagainst perforations 18 in face sheet 17 by the action of the gas flow.Therefore, it has been found that by unifying these materials asdescribed above into quilted lamination 19, a protective agent isproduced which, on the one hand, protects sound blanket 12 from beingdestroyed by the erosive forceof high velocity gas streams and yet, onthe other hand, is sufficiently transparent to the passage of soundpressure waves to enable their entry to and dissipation in blanket 12.

A modification of the preferred embodiment is shown in FIGURES 4, 5, and6 wherein the panel construction shown is identical with that in FIGURES1, 2, and 3 with the exception that lamination 228 though still composedof glass fiber cloth 29 interposed between close mesh wire screens 31and 3 2. is integrated into panel 33 in a different manner. Instead ofbeing stapled together in quilt-fashion, glass fiber cloth 29 andscreens 31 and 32 are joined together and to the face sheet 34 by meansof rivets 36 passing through all layers of the lamination 228 and alsothrough the face sheet 34. In a typical application of this modifiedform of the invention, rivets 36 and the accompanying washers 37 areplaced on approximately six inch centers in both directions.

Whether the velocity protective lamination be of quilted constructionand supported only along its edges or whether it be fastened by means ofriveting as in FIG- URES 4, 5, and 6 the same function is performedthereby. Thus, as the gas stream strikes the face of the acousticalpanel the effective flow resistance of the lamination serves either totdefiect thehigh velocity gases or at least to reduce their velocity.Since the prime function of an acoustical panel is to absorb sound,however, any construction which would hinder the performance of thisfunction would involve an objectionable compromise.

Fortunately, the present arrangement enables the' choice of a designflow resistance not only giving the necessary protection under sustainedexposure to gas fiow velocitices in excess of 300 f.p.s., but alsoenabling the entry of sound energy for its dissipation by blanket 12.Also, due to the particular selection of materials employed in thislamination, it has been found that the acoustical qualities of soundblanket 12 are actually in1- proved by combination with the acousticalresistance of the lamination with the net result that a more effectiveacoustical panel is produced thereby.

This enhancement of the acoustical properties of blanket 12 by the useof the present velocity protective lamination is an interestingphenomenon in that the laminated construction either d9 or 23 actuallydetunes the panel to receiving lower frequency vibrations. Thisdc-tuning by the laminated construction actually shifts the entire soundabsorptive effect of the panel as an entity by /2 to 1 full octave'intothe lower frequencies of vibration in which range blanket 12 possessesgreater ability to absorb or dissipate sound. Thus, by employing thisunique construction having an acoustical resistance of 37 rayls locatedimmediately under per-' forations 13 serving to increase the effectiveacoustical resistance of perforations 18 by a critically small amountthe inventors have produced an acoustical panel with enhanced acousticalperformance in low frequency sound reduction and, at the same time, anefficient protective measure against the erosion of itssound-dissipating medium.

Since the panel construction illustrated has only one perforated facesheet per panel, only one protective lamination is required. In cases inwhich such panels are constructed with perforated faces on each sidethereof two protective laminations would be used per panel, one undereach face sheet. Panels of such dual-faced construction, as statedbelow, are used for installations in which the panels are arranged inspaced parallel relationship to permit gas flow therebetween.

Obviously, many modifications'and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood, that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed:

1. A device for the attenuation of sound energy in high velocity gasflow comprising in combination an enclosure, sound dissipating materialdisposed within said enclosure, a portion of the outer surface of saidenclosure being (perforate, at least three layers of a plurality ofdissimilar flexible meshed fabrics transparent to sound pressure wavesmounted between said perforate portion and said sound dissipatingmaterial and means for joining said laminates in a plurality ofpositions spaced over the surface thereof to form a unitary lamination.

2. A device for the attenuation of sound energy in gas flows withvelocities in excess of 209 fps. comprising in combination an enclosure,sound dissipating material disposed within said enclosure, .a portion ofthe outer surrfiace of said enclosure being perforate for thecommunication of sound energy from the exterior to the interior of saidenclosure, at least three layers of a plurality of dissimilar flexiblemeshed .fiabrics transparent to sound pressure Waves located betweensaid perforate portion and said sound dissipating material and means forfastening said laminates together over the surface thereof in aplurality of spaced positions to form a unitary lamination.

3. A device for the attenuation of sound energy substantially asdescribed in claim 1 wherein the unitary lamination is composed of alaminate of glass fiber cloth interposed between two laminates of closemesh wire screen.

4. A device for the attenuation of sound energy substantially asdescribed in claim 3 wherein the unitary lamination has an acousticalresistance in the range from 3 to 7 trayls.

5. A device for the attenuation of sound energy substantially asdescribed in claim 3 wherein the laminates are assembled into a quiltedunitary lamination by multiple joining means placed in spacedrelationship.

6. A device for the attenuation of sound energy substantially asdescribed in claim 2 wherein the unitary lamination is composed of alaminate of glass fiber cloth interposed between two laminates of closemesh wire screen.

7. A device for the attenuation of sound energy substantially asdescribed in claim 6 wherein the unitary lamination has an acousticalresistance in the range from 3 to 7 rayls.

8. A device for the attenuation of sound energy substantially asdescribed in claim 6 wherein the laminates are assembled into a quiltedunitary lamination by multiple joining means placed in spacedrelationship.

9. A device for the attenuation of sound energy substantially asdescribed in claim 2 wherein the plurality of laminates are attached tothe perforate portion :by multiple joining means arranged in spacedrelationship.

10. In a device for the attenuation of sound energy in high velocity gasflow wherein a portion of the outer surface of the enclosure of thedevice is perforate for the communication of sound energy to sounddissipating material disposed within the enclosure so as to absorb thesound energy, the improvement comprising means disposed between saidperforate portion and said sound dissipating material for reducing thevelocity of gases reaching said sound dissipating material whereby saidsound dissipating material is protected from erosion, said meanscomprising a layer of glass fi'ber cloth interposed between two layersof close mesh wire screen, said layers being joined over a surfacethereof in a plurality of spaced positions.

11. A unified lamination substantially as described in claim 10 whereinthe layers are joined by multiple fastenin'gs arranged in a quiltedarrangement.

12. A unified lamination substantially as described in claim 10 havingan acoustical resistance in the range from 3 to 7 rayls.

References Cited in the file of this patent UNITED STATES PATENTS1,387,391 Hall Aug. 9, 1921 2,065,751 Scheldorf Dec. 29, 1936 2,514,170Walter et al. July 4, 1950 2,595,047 Beranek Apr. 29, 1952 2,726,977 Seeet al. Dec. 13, 1955 2,826,261 E-ckel Mar. 11, 1958 2,838,806 SabineJune 17, 1958 2,918,984 Lerrunernran Dec. 29, 1959 2,935,151 Watters etal. May 3, 1960 2,940,537 Smith et al. June 14, 1960 OTHER REFERENCESNoise Control (magazine): Porous Materials for Noise Control, by SamuelLabate, issue of January 1956, pages 15-19 and 72.

1. A DEVICE FOR THE ATTENUATION OF SOUND ENERGY IN HIGH VELOCITY GASFLOW COMPRISING IN COMBINATION AN ENCLOSURE, SOUND DISSIPATING MATERIALDISPOSED WITHIN SAID ENCLOSURE, A PORTION OF THE OUTER SURFACE OF SAIDENCLOSURE BEING PERFORATE, AT LEAST THREE LAYERS OF A PLURALITY OFDISSIMILAR FLEXIBLE MESHED FABRICS TRANSPARENT TO SOUND PRESSURE WAVESMOUNTED BETWEEN SAID PERFORATE PORTION AND SAID SOUND DISSIPATINGMATERIAL AND MEANS FOR JOINING SAID LAMINATES IN A PLURALITY OFPOSITIONS SPACED OVER THE SURFACE THEREOF TO FORM A UNITARY LAMINATION.